Use git on an untrusted server via a GPG-encrypted repository.
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LICENSE
README.md
git-gpg
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README.md

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git-gpg

git-gpg provides git-based, GPG-encrypted distributed version control. Specifically, it is useful for collaborating with other trusted endpoints through semi-trusted or untrusted middle-points (e.g., through a VPS on the cloud).

At a high level, it encrypts the data objects in your .git directory, and then uploads those files to a remote directory using rsync-over-ssh. Simple.

More specifically:

When you push changes, git-gpg...

  1. Pushes your local changes into the staging repository.
  2. Encrypts the .git database files in the staging repository.
  3. Runs rsync to upload the encrypted .git database files to the remote server.

When you pull changes, git-gpg...

  1. Runs rsync to download encrypted .git database files from a remote server to a local directory.
  2. Decrypts the .git database files to form a "staging" repository.
  3. Pulls from the staging repository into your local repo.

Requirements

To try git-gpg you will need:

  • A recent version of git. Tested with 1.9.1.
  • A recent version of gpg. Tested with 1.4.16.
  • A recent version of rsync. Tested with 2.6.9.
  • A gpg private key. For help, see the gpg cheat sheet.
  • A git repository.

Installation

Copy the git-gpg script to a directory in your path.

Usage

Setup

Add a GPG-encrypted remote repository:

git gpg add myremote user@server:~/files/project.gpg

Add one or more GPG recipients:

git gpg add-recipient myremote you@host1
git gpg add-recipient myremote friend@host2
...

Show information about a GPG-encrypted repository, including recipients and branches:

git gpg show myremote

Push

Push to the GPG-encrypted repository:

git gpg push myremote master

You can use the standard git command line options when pushing.

git gpg push --verbose myremote master

For example, specify the local branch and the remote branch.

git gpg push myremote local-branch:remote-branch

Delete a branch.

git gpg push myremote :branch-to-delete

Pull

Pull from the GPG-encrypted repository:

git gpg pull myremote

You can use the standard git command line options when pulling.

git gpg pull --rebase myremote

For example, you can specify the remote branch and local branch.

git gpg pull myremote remote-branch:local-branch

Cautions

  1. git-gpg has not been thoroughly tested with every edge case. We make no guarantees of safety.
  2. git-gpg is a sledgehammer approach -- it encrypts your entire repository. If a user only need to encrypt one or two files containing security keys, git-gpg is probably not the right solution.
  3. git-gpg requires the user to learn new (and sometimes confusing) commands.
  4. git-gpg does not play well with existing social coding tools like GitHub. (That said, the goal of git-gpg is to prevent others from reading code, not encourage it.)
  5. git-gpg does not use git as a storage mechanism on the remote endpoint.

Other Approaches / Prior Art

We experimented with a number of other solutions before arriving at this version of git-gpg, including the following:

Git Clean / Smudge Filters

Git provides a "clean filter" that will run right before a file is committed, and a "smudge filter" that will run right after a file is checked out. One of the intended use cases is to transform files from Unix line endings to and Windows line endings and vice versa.

Some clever folks have hacked this so that the client filter decrypts a file, and the smudge filter encrypts the file. While this is clever, it is not recommended:

If your "clean" encrypts and "smudge" decrypts, it means you are refusing all the benifit git offers. You are making a pair of similar "smudged" contents totally dissimilar in their "clean" counterparts. That is simply backwards.

The git-remote-gcrypt Project

Another approach involves a remote helper. The git-remote-gcrypt code is difficult to follow, but as far as we can tell, it creates a git repository inside of another git repository. The inner git repository stores encrypted packfiles. The outer repository is used simply for a transport mechanism. That may be totally wrong, as the code is quite complex.

There are two ways of constructing a software design: One way is to make it so simple that there are obviously no deficiencies, and the other way is to make it so complicated that there are no obvious deficiencies.

Tony Hoare - winner of the 1980 Turing Award. http://en.wikiquote.org/wiki/C._A._R._Hoare

We don't trust software that is too complex. The lead developer seems to share some of this sentiment:

I hope it interests someone, and maybe it even reaches the target of being both usable and secure. It also helps me if you point out if/how/why it is broken(!).

Ulrik Sverdrup - Author of git-remote-gcrypt https://groups.google.com/forum/#!topic/git-users/0nm3lP122K0

An Encrypted Remote FileSystem

Another approach is to store the remote git repo on an encrypted filesystem, and then mount it when pushing or pulling code. An intruder must time their attack to happen when the code is decrypted in memory. This raises the difficulty level, but still leaves a significant weak surface. If you are truly paranoid about your code, then it's dangerous to ever decrypt it anywhere except for on your own computer.

Encrypted Patches

A previous version of this utility attempted transmit and store encrypted code patches. The was more bandwidth efficient than the current git-gpg approach, but it had two main disadvantages:

  • Patches don't preserve the commit hash, so different consumers of the repo saw different hashes.
  • It is possible to have a valid git repository that cannot be re-created by exporting and re-applying all of its constituent patches in order.

The second disadvantage was obviously a show-stopper.

Licence

git-gpg is released under the MIT License.

Copyright (c) 2016 GlassRoom Software LLC.